The fiancee of a man who claimed to be Henry Ford's illegitimate grandson has told a court she only discovered his secret life of prostitutes and drugs when she found him murdered in their home.

The blood-soaked body of John Dahlinger was found by his long-term fiancee Melanie Yanchuk in their marital bed at their condominium in Grand Rapids, Michigan.

Pimp Danyell Thomas, 37, is accused of conspiring with a prostitute to drug and rob the 56-year-old before shooting him dead.

Dahlinger's late father has always claimed he was the illegitimate son of Henry Ford following an alleged affair the car manufacturer had with his young secretary.

Murder: John Dahlinger, 56, was found dead in his bed by his longtime fiancee Melanie Yanchuk at their condominium in Grand Rapids, Michigan (both pictured)

Accused: Danyell Thomas (left) is accused of murdering Dahlinger in October 2013. He was allegedly shot after he could not pay prostitute Dijana Kilic (right) after she performed a strip tease at his home

In court Yanchuk wept as said she far as she knew her partner, a father-of-two, did not use drugs and did not use prostitutes.